Police officers need improved training on how they ''hog tie'' prisoners and use restraints, a new report says.

Additionally, those working with youth offenders were failing to keep records on how many times restraints were used.

The use of mechanical restraints in New Zealand detention facilities was highlighted in the Monitoring Places of Detention Annual report, which includes information about youth residential facilities, police custody facilities, prisons and health and disability detention units.

One police district received three complaints about its officers' use of mechanical restraints - which excluded handcuffs - between July 2011 and June this year.

Those complaints, and other findings from the Independent Police Conduct Authority (IPCA), prompted recommendations for improved training in the use of restraints, and for officers who dealt with people who were mentally impaired.

People in police custody were sometimes mechanically restrained with a restraint board, which has chest, arm and leg straps.

They may also be restrained by combined rear wrist and ankles restraints, commonly known as a "hog tie".

Mechanical restraints, under law, are to be used as a last resort to immobilise a person who cannot be restrained otherwise, and the Human Rights Commission said their use equated to ill treatment if they were used inappropriately or for days at a time.

The commission said the boards represented "a significant interference with individual rights and freedoms" and that restraints required "stringent safeguards and restrictions around their use".

They "should never be used as a punishment or to compensate for shortages of trained staff".

A police spokesman said police were in the process of developing further training on mechanical restraints, following the IPCA's recommendations.

Some staff received training on the use of mechanical restraints, such as the boards, at a district level, while all staff received ongoing training on the use of restraint techniques, such as handcuffs.

Police were also trialling the use of restraint chairs, which may be a safer option, the spokesman said.

In response to the IPCA's recommendations, one district commander had reviewed its systems, including further training for investigators of complaints, and had discontinued the use of mechanical restraint boards until there was national mandated training.

The district which was the subject of complaints and the district which had reviewed its systems had not been named.

A review of detention facilities for youth also raised questions about the use of restraints.

The Office of the Children's Commissioner monitored residences where some youth offenders were held and said there were gaps in the recording of the use of restraints and searches.

"Given that these are the most restrictive interventions that Child, Youth and Family and Barnados can carry out, this documentation must be able to account for these interventions," a report by the office said.

The use of restraints in health and disability detention facilities, however, seemed to be phasing out as many units have installed - or are in the process of installing - sensory modulation rooms, the Ombudsman's office said.

These rooms were used to calm people who are agitated or stressed, and were an alternative to the use of restraints.

The Department of Corrections was also reviewing its use of restraints as part of the Corrections Amendment Bill, which was awaiting its second reading in Parliament.

A Visiting Justice - a District Court judge - was currently required to give Corrections permission to use a mechanical restraint for more than 24 hours, but the bill, if passed, would allow for a prison manager to make that decision, with input from a medical officer.

The Human Rights Commission, the Ombudsman and Just Speak opposed the removal of the role of a Visiting Justice, arguing that retaining the role retained "independent oversight".